1. Field of the Invention
The present invention relates generally to an electronic circuit and an electronic device including the same, and more specifically to an electronic circuit including a storage unit to hold information in a nonvolatile manner, and an electronic device including the electronic circuit.
2. Description of the Background Art
A pulse counter counts how many pulses are received. Japanese Patent Laying-Open No. 2007-104020 discloses an example of a pulse counter.
The pulse counter of Japanese Patent Laying-Open No. 2007-104020 includes a common input terminal, a common input circuit, a comparator circuit, a hold circuit, a reset circuit, a level determination unit, a reset signal generation unit, and a count unit. The common input terminal is connected to a first or second cable. The first cable is connected to an output terminal of another device. The other device is provided with a no-voltage contact outputting a pulse therefrom. Furthermore, the second cable is connected to an output terminal of an externally provided current transformer. In this current transformer, the pulse output from the no-voltage contact provided in the other device is detected.
The common input circuit is connected to the common input terminal and thus accommodates both an output from the other device and that from the current transformer. The comparator circuit receives an output of the common input circuit and a set reference potential. The hold circuit holds the high (H) level of an output of the comparator circuit. The reset circuit resets the output of the comparator circuit held by the hold circuit. The level determination unit determines the output in level of the comparator circuit held by the hold circuit. The reset signal generation unit outputs a reset signal to the reset circuit when the level determination unit outputs an H level determination signal. The count unit counts the H level determination signal. The above configuration allows a pulse received from the other device and that received from the current transformer to be received via a common input terminal if the pulses are received in different systems, respectively.
Generally, a pulse counter includes a microcomputer or dedicated counter integrated circuit (IC), a clock oscillator, and a nonvolatile memory. The clock oscillator supplies a clock signal to the microcomputer. The nonvolatile memory holds a count value in a non-volatile manner. The nonvolatile memory is for example an electrically erasable programmable read-only memory (EEPROM).
When the pulse counter is powered on, the clock oscillator supplies the clock signal to the microcomputer. This allows the microcomputer to perform a count processing. Initially, the microcomputer reads a count value held in the EEPROM. A pulse or count signal is then supplied to the microcomputer. The microcomputer performs the count processing based on the count value and the count signal. A result of the count processing is stored to the EEPROM.
When the pulse counter is powered on, the clock oscillator starts to oscillate. However, it requires some time before the clock oscillator provides steady operation. Furthermore, it also requires some time to read/write from/to the EEPROM. A typical pulse counter thus requires some time after it is powered on before writing to the EEPROM is completed.
Generally, conventional electronic circuits cannot perform signal processing after the electronic circuit receives voltage from a power supply before some period of time elapses. Accordingly, a voltage signal (e.g., a count signal) applied to start signal processing must be supplied to the electronic circuit from an external circuit some period of time after the electronic circuit has received voltage from the power supply.